Tip and ring
Encyclopedia
"Tip" and "Ring" are common terms in the telephone service industry referring to the two wires or sides of an ordinary telephone line
. Tip is the ground side (positive
) and Ring is the battery (negative
) side of a phone circuit. In the UK these are referred to as the 'A' (earth) and 'B' (battery) wires. The ground side is common with the central office of the telephone company
(telco); the battery side carries −48 volts of DC voltage when in an "idle" or "on hook" state (nominally -50 volts in the UK). The combination of tip and ring, then, makes up a normal phone line circuit, just as a car's battery needs both connections leads to have a complete electrical circuit. To ring the phone to alert to an incoming call, about 90 volts of 20 Hz AC current is superimposed over the DC voltage already present on the idle line.
In the early telephone years of rotary dial
, tip and ring wire reversal was of little consequence, except for a party line with selective ring. Then came DTMF or Touch Tone. Because the tone generator is electronic, tip and ring had to be in the correct order at any given phone jack in order to be able to make outgoing calls with a Touch Tone phone. If they were reversed in polarity, there would still be a dialtone and calls could be received, but not dialed out. In most phones manufactured in the late 20th century, a diode bridge
eliminates that problem. Today, tip and ring reversal is mostly immaterial, except for special circuits including DID (Direct Inward Dialing
) trunks, T-1 lines
, and ground start
lines where the field side ("terminal") equipment--a company's PBX switch, for example--can only function correctly with correct tip and ring polarity.
See POTS
and PSTN for more details on telephone networks.
, which were used in the early days of telephony with operators handling customer calls. The names of the wires are derived from the part of the plug to which they are connected. Tip and Ring are often abbreviated as T and R in wiring diagrams. However, when so abbreviated, T and R are often mistakenly interpreted as Transmit and Receive.
While the ring is connected to -48 volts, the tip is connected to ground for safety. This is because when the telephone operator is handling the plug, the tip is more likely to touch something other than intended. With the tip as ground, nothing dangerous will happen.
is adjusted to between 50 and 52 volts, but the nominal voltage is still used in documents and designations.
In the middle 20th century, long loops in many rural areas of North America used range extenders, which operated at 100 or 130 volts to ensure reliable signaling. Some rural switching systems were designed to apply range extenders internally and thus share a few extenders among many lines, while for other lines the extender was an external applique per line.
Originally, the voltages on the wires were positive with respect to earth. This is called negative ground, since the negative side of the battery is grounded to earth. Then engineers discovered that with positive voltage on the copper wires, copper wires age quickly, due to electrolysis
. With negative voltage on the wires, in respect to earth, (called positive ground) the copper is protected from corrosion. This is referred to as cathodic protection
.
is color coded, two-wire telephone plug
s or the first pair of a multipair plug commonly have the tip wire coded green and the ring red. In four wire plugs, the second pair are black tip and yellow ring. For a third pair, white and blue. For larger numbers of wires, more complex schemes such as the 25-pair color code
are used.
Telco technicians often used the phrase "red-right-ring-rear" (or "ring-right-red-rough") to remember that the red wire connects to the right-side post in the wall jack and to the ring on the plug and to the rear lug on main distributing frames. Sometimes "rough" or "ridge" was added for jumper wires with a tactile code.
Telephone line
A telephone line or telephone circuit is a single-user circuit on a telephone communication system...
. Tip is the ground side (positive
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
) and Ring is the battery (negative
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
) side of a phone circuit. In the UK these are referred to as the 'A' (earth) and 'B' (battery) wires. The ground side is common with the central office of the telephone company
Telephone company
A telephone company is a service provider of telecommunications services such as telephony and data communications access. Many were at one time nationalized or state-regulated monopolies...
(telco); the battery side carries −48 volts of DC voltage when in an "idle" or "on hook" state (nominally -50 volts in the UK). The combination of tip and ring, then, makes up a normal phone line circuit, just as a car's battery needs both connections leads to have a complete electrical circuit. To ring the phone to alert to an incoming call, about 90 volts of 20 Hz AC current is superimposed over the DC voltage already present on the idle line.
In the early telephone years of rotary dial
Rotary dial
The rotary dial is a device mounted on or in a telephone or switchboard that is designed to send electrical pulses, known as pulse dialing, corresponding to the number dialed. The early form of the rotary dial used lugs on a finger plate instead of holes. Almon Brown Strowger filed the first patent...
, tip and ring wire reversal was of little consequence, except for a party line with selective ring. Then came DTMF or Touch Tone. Because the tone generator is electronic, tip and ring had to be in the correct order at any given phone jack in order to be able to make outgoing calls with a Touch Tone phone. If they were reversed in polarity, there would still be a dialtone and calls could be received, but not dialed out. In most phones manufactured in the late 20th century, a diode bridge
Diode bridge
A diode bridge is an arrangement of four diodes in a bridge circuit configuration that provides the same polarity of output for either polarity of input. When used in its most common application, for conversion of an alternating current input into direct current a output, it is known as a...
eliminates that problem. Today, tip and ring reversal is mostly immaterial, except for special circuits including DID (Direct Inward Dialing
Direct Inward Dialing
Direct inward dialing , also called direct dial-in in Europe and Oceania, is a feature offered by telephone companies for use with their customers' private branch exchange systems...
) trunks, T-1 lines
T-carrier
In telecommunications, T-carrier, sometimes abbreviated as T-CXR, is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America, Japan, and South Korea....
, and ground start
Ground start
In telephony, a ground start or GST is a method of signaling from a terminal or subscriber local loop to a telephone exchange, in which method a cable pair is temporarily grounded to request dial tone...
lines where the field side ("terminal") equipment--a company's PBX switch, for example--can only function correctly with correct tip and ring polarity.
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
and PSTN for more details on telephone networks.
Origin of the term tip and ring
The terms Tip and Ring originated from the telephone operators' phone plugTRS connector
A TRS connector is a common family of connector typically used for analog signals including audio. It is cylindrical in shape, typically with three contacts, although sometimes with two or four . It is also called an audio jack, phone jack, phone plug, and jack plug...
, which were used in the early days of telephony with operators handling customer calls. The names of the wires are derived from the part of the plug to which they are connected. Tip and Ring are often abbreviated as T and R in wiring diagrams. However, when so abbreviated, T and R are often mistakenly interpreted as Transmit and Receive.
While the ring is connected to -48 volts, the tip is connected to ground for safety. This is because when the telephone operator is handling the plug, the tip is more likely to touch something other than intended. With the tip as ground, nothing dangerous will happen.
Negative 48 volts
The voltage applied to the telephone wires is related to the distance at which the telephone can be operated. Higher voltage can signal to greater distance. High voltage, however, presents a hazard to both customers and technicians. Thus 48 volts is a compromise between safety and distance. Usually central office common batteryCommon battery
In telecommunication, a Common battery is a single electrical power source used to energize more than one circuit, electronic component, equipment, or system....
is adjusted to between 50 and 52 volts, but the nominal voltage is still used in documents and designations.
In the middle 20th century, long loops in many rural areas of North America used range extenders, which operated at 100 or 130 volts to ensure reliable signaling. Some rural switching systems were designed to apply range extenders internally and thus share a few extenders among many lines, while for other lines the extender was an external applique per line.
Originally, the voltages on the wires were positive with respect to earth. This is called negative ground, since the negative side of the battery is grounded to earth. Then engineers discovered that with positive voltage on the copper wires, copper wires age quickly, due to electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
. With negative voltage on the wires, in respect to earth, (called positive ground) the copper is protected from corrosion. This is referred to as cathodic protection
Cathodic protection
Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. The simplest method to apply CP is by connecting the metal to be protected with another more easily corroded "sacrificial metal" to act as the anode of the...
.
Color code
When simple on-premises wiringOn-premises wiring
In telecommunication, on-premises wiring is customer-owned communications transmission lines. It is also called customer premises wiring . The transmission lines can be metallic or optical fiber, and may be installed within or between buildings.Premises wiring may consist of horizontal wiring,...
is color coded, two-wire telephone plug
Telephone plug
A telephone plug is a type of male connector used to connect a telephone to the telephone wiring in a home or business, and in turn to a local telephone network. It is inserted into its female counterpart, a telephone "jack", commonly affixed to a wall or baseboard...
s or the first pair of a multipair plug commonly have the tip wire coded green and the ring red. In four wire plugs, the second pair are black tip and yellow ring. For a third pair, white and blue. For larger numbers of wires, more complex schemes such as the 25-pair color code
25-pair color code
The 25-pair color code is a color code used to identify individual conductors in a kind of electrical telecommunication wiring for indoor use, known as twisted pair cables . The colors are applied to the insulation that covers each conductor...
are used.
Telco technicians often used the phrase "red-right-ring-rear" (or "ring-right-red-rough") to remember that the red wire connects to the right-side post in the wall jack and to the ring on the plug and to the rear lug on main distributing frames. Sometimes "rough" or "ridge" was added for jumper wires with a tactile code.